Wednesday, October 19, 2011

Winter Forecast! La Nina...Cold Winter Witch

This beautiful graph is the 5-day temperature mean of the waters over the Pacific Ocean. Buoys in the Pacific record the temperatures on the hour. The data is sent to NOAA and recorded.

I took a picture of a similar buoy at the Museum of Science and Industry in Chicago. It is used to collect data of wave heights for tsunami events...but is similar to the floating recorders used to take the water temperature in the ocean.

La What?

Right now we are in a La Nina event. La Nina is Spanish for "the girl". In weather geek terms it means the water in the Pacific is cooler than normal.

El Nino...Spanish for "the child". Means warmer waters over the Pacific Ocean.

What the heck does it all mean for Iowa? Good question.

In La Nina years we usually have colder than normal temperatures during the winter months. Over the southern 1/2 of Iowa wetter than normal winters can be expected. Drier than normal winters are common for the northern 1/2 of the state.

Notice how we are split in half? These mid-latitudes are great for seasonal change, but murder when forecasting who is going to be slammed with snow during La Nina years.

Here are the forecast maps for November through January. (All maps are provided by National Weather Service Climate Prediction Center.)

You can see we have equal chances (EC) of above or below average temperatures or snowfall. There is a slight chance for above average precipitation over the extreme southeastern corner of the state....but just for about 3 or 4 counties in Iowa. It really doesn't look that bad. In fact in La Nina years we usually have a pretty mild end of fall and start to winter.

Now check out the forecast maps for January, February and March. The two lower maps.

For the January through March period we see a mostly equal chance of average snow and a greater chance for below normal temperatures over the northern counties.

Last year we had our 34th coldest winter and 9th snowiest winter. It was the 5th straight snowier than normal winter...and the 4th straight that was colder than normal. We only had about 3 inches more snow than average in Des Moines. It was nothing like the 2009-2010 season that left us with a near record 69+ inches of snow.

The Winter Weather Wrap....Ed's Prediction.

La Nina is not particularly strong this year...but is trending cooler. So I agree with the equal chances of just above or just below the average snowfall this year in Des Moines. So expect to move about 33 to 35 inches of snow. This is better than 69 inches of winter wonderland, but much of the state is under a mild to moderate drought conditions. We could use some rain now and some snow to melt into water tables next spring.

Temperatures are easier to read with a weak La Nina. It will be cooler than normal. The jet stream will be farther south this winter. It will keep us cooler than average and it should send more precipitation south of Iowa. It could be really good news for the drought-ridden states of Kansas, Oklahoma and Texas.

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